Don't Fertilize, Neutralize

It’s coming: a male contraceptive that isn’t sold in rest-room vending machines. No fewer than three male birth control methods are presently being tested. In a nine-country study published last April, weekly injections of testosterone prevented conception in 98.6 percent of 399 couples. An outside source of testosterone fools the pituitary into thinking the testes are making too much of the hormone. In response, the pituitary stops releasing two other hormones that stimulate sperm and testosterone production, and the sperm count drops to nil.

Physical side effects are thus far minimal: mild acne and a few pounds of weight gain. But do the injections turn men into macho jerks? Everybody’s partner thinks they’re jerks once in a while, so it’s a little hard to sort that out, says study coauthor William Bremner of the Veterans Affairs Medical Center in Seattle. If you take a bunch of normal men and their partners, and you put the men on testosterone injections, which the whole society thinks does something to aggression, and a guy is a jerk two months later, then people will leap to the conclusion that the injections were responsible.

The biggest drawback so far appears to be the weekly injection, described by one researcher as a painful shot in the buttock. Bremner says the researchers are moving toward an oral medication, or at least a shot that would last several months. An informal poll of male science journalists conducted last October, however, suggested that a birth control method involving painful shots, even infrequent ones, would be unlikely to be widely adopted.

Meanwhile, other research is focusing on ways to foil sperm in their efforts to break through the zona pellucida, the egg’s gel-like protective coating. To fertilize an egg, a sperm latches onto this coating by means of a protein on its head, which then locks onto a protein on the egg. This coupling of proteins releases a caustic enzyme that eats through the zona pellucida, clearing the way for fertilization. One way to stymie sperm is to engage the enzyme with a decoy zona pellucida compound so there’s none available to assault the real thing. Tests on one such compound, carried out by biochemist Joseph Hall at North Carolina State University and published this past May, reduced enzyme activity in rats by 95 percent and blocked fertilization 92 to 98 percent of the time. Human trials have just begun.

Another option under investigation is to block the protein receptors on the sperm, so sperm can’t dock on the egg’s exterior. With long-term safety data and approval by the Food and Drug Administration yet to come, though, a male pill of any kind is a number of years off. Then there’s what Hall calls the sexist twist. Ninety percent of the scientists in this field are male, he says. And males are, in general, a little less likely to push the product.